共查询到17条相似文献,搜索用时 109 毫秒
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以水合氟化钆为原料,氟化氢铵为添加剂,研究了脱水—转化法制备低氧氟化钆过程中氟化氢铵的作用及其氧含量的变化规律。结果表明,氟化氢铵在脱水过程中可以抑制水合氟化钆发生水解反应,在转化过程中可以将水解产物GdOF转化为GdF_3;在脱水后的物料中加入7%的氟化氢铵,产物中的氧含量可降低到0.09%;在一定温度和压力范围内,氟化钆中的氧含量随脱水温度、转化温度以及压力的升高而降低,300℃、300 kPa时达到最低值;转化过程中充入氩气可使氧含量达到0.088%。 相似文献
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以氧化钆和氟化氢铵为原料,通过X射线衍射、化学分析和实际观察,确定了反应过程中的产物,研究了该体系在不同条件下的反应规律,制定了新的GdF3制备工艺。常压下,粉状Gd2O3与NH4HF2在100℃开始反应,生成GdNH4F4,NH4F,NH3和H2O。224℃时GdNH4F4分解为GdF3和NH4F,NH4F在156—430℃间挥发和分解。反应过程包括合成、分解和脱铵3个反应环节。真空可以降低每一步反应的起、止温度,特别有利于脱铵反应进行。用氟化氢铵制备氟化钆应采用“常压低温合成-真空中温分解.真空高温脱铵”工艺:即压力为101kPa,温度为185℃合成GdNH4F4;压力小于10.1kPa,温度为210℃分解GdNH4F4;压力小于10.1kPa,温度为385℃脱除NH4F。 相似文献
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结合本地区锌精矿的特点和生产实际需求,在参考锌精矿测定锌量国标方法的基础上建立了锌精矿中锌量的快速测定方法。试样经盐酸、硝酸、硫酸、高氯酸分解后,氟化氢铵消除硅,铅生成硫酸铅沉淀,过硫酸铵氧化锰成二氧化锰沉淀,饱和氟化氢铵掩蔽三价铁,硫代硫酸钠掩蔽铜,氟化钾掩蔽铝,碘化钾掩蔽镉,以二甲酚橙为指示剂,在PH=5~6的六次甲基四胺缓冲溶液中,用EDTA标准溶液滴定至溶液由红色变为亮黄色为终点,测定结果即为锌量。该方法无需沉淀过滤分离铁,避免了氢氧化物铁沉淀对锌的吸附和包裹,操作过程简单、快速,分析结果准确可靠,更好的满足了生产实际的需求。 相似文献
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探讨了水蒸汽蒸馏分离-富集氟的条件,建立了EDTA滴定法测定氟化镝中氟量的方法。试样经高氯酸分解后,在140~170 ℃的温度下进行水蒸汽蒸馏,溶液中的氟富集于馏分中,在较低的pH值条件下煮沸馏分使氟离子与过量的氯化镧充分反应,待溶液冷却后,以二甲酚橙为指示剂,六次甲基四胺-盐酸为缓冲溶液,用EDTA标准溶液滴定溶液中剩余镧离子,计算得出氟量。干扰试验证明,样品中的稀土、铁、钙、铝、硅等干扰元素可有效与氟分离,对实验结果无影响。方法用于氟化镝中氟量的测定,结果的相对标准偏差(RSD,n=10)为0.48%。对氟化镝实际样品进行分析,结果同碱熔融-EDTA滴定法一致。 相似文献
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在pH=3的NH_4HF_2介质中,利用微量Mn~(2+)催化MnO_4~-与甲基橙反应,建立分光光度法测定特种铁合金中的微量锰,该方法快速准确,是测定相应铁合金中微量锰元素的较好测定方法。 相似文献
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《中国稀土学报(英文版)》2020,38(8):883-890
A series of supported CeO_2/TiO_2 catalysts were prepared to explore the influence of CeO_2 loading on these catalysts for the selective catalytic reduction of NO_3 by NH_3(NH_3-SCR).The catalysts were investigated in detail by means of XRD,Raman,H_2-TPR,NH_3-TPD,XPS,in situ DRIFTS,and NH3-SCR reaction.The activity of the catalyst is closely related to the content of CeO_2.When the loading of CeO_2 is near the dispersion capacity(1.16 mmol Ce~(4+)/100 m~2 TiO_2),the catalytic activity is better.This may be because that the dispersed CeO_2 is the active species and the catalyst has appropriate redox property,along with the larger amounts of surface Ce content and surface adsorbed oxygen species.Finally,a possible reaction mechanism via the Langmuir-Hinshelwood(L-H) mechanism is tentatively proposed to further understand the NH_3-SCR reaction. 相似文献
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硫代硫酸盐提金理论研究—金溶解动力学 总被引:6,自引:2,他引:4
采用腐蚀电化学方法研究了金在硫代硫酸盐溶液中溶解的动力学。无铜、氨时,金的溶解活化能为27.99kJ/mol,Cu(NH_3)_4~(2+)为0.01mol/L,总氨浓度为0.5mol/L时活化能降为15.54kJ/mol;在0.001~0.1mol/L范围内,Cu(NH_3)_4~(2+)的反应级数为1。动力学研究的结果进一步揭示了铜、氨在浸金过程中的催化作用,并再次证实了作者提出的氨性硫代硫酸盐溶液浸金的电化学—催化机理。 相似文献
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应用同时平衡原理和质量平衡原理对SnCl4-NH4Cl-HCl-H2O体系进行了热力学分析和计算,对于无法收集的相关(NH4)2SnCl6的热力学数据进行了估算,在此基础上绘制了SnCl4-NH4Cl-HCl-H2O体系在标准状态下各相关物种和pH之间的关系曲线。结果表明,溶液中的总铵浓度和体系的pH值是影响(NH4)2SnCl6或Sn(OH)4存在的重要参数。在该体系中,增大体系的酸度到6nol/L以上,体系中的Sn^4 既以(NH4)2SnCl6形式沉淀出来,这就为直接由含锡原料提取纯(NH4)2SnCl6,并用以取代SnCl4来制备ATO或ITO粉体提供了理论依据。 相似文献
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以MgF2晶种为成核剂的NH4F沉淀法去除硫酸锰中的杂质镁已取得很好的效果。考察了温度、反应时间和pH等因素对镁沉淀率的影响。结果表明,提高温度和pH有利于提高镁除去率,而反应时间在1h内镁除去率随时间增加而提高,1h后镁除去率基本不变。 相似文献
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Hongcheng Zhang Dairui Xie Heng Zhang Meng Jiang Hao Huang Yu Wan Yang Liao Shilin Zhao 《中国稀土学报(英文版)》2021,39(2):186-193
The bastnaesite used in hydrometallurgy usually contains 7%-11% fluorine,and the conversion of fluorine into high-value products is the key to achieving green production of rare earths and improving the comprehensive utilization of bastnaesite.In order to recover fluorine from bastnaesite in the form of KBF4,the mechanism of F-conversion to BF4-in sulphuric acid leaching solution of roasted bastnaesite was studied by using Eh-pH diagram and simulation experiment.It shows that the formation of BF4-is affected by pH in the absence of rare earths.BF4-is hydrolyzed to BF3 OH-and F-when the pH is greater than 3.9,and part of F-exists as HF2-when pH is lower than 2.In the presence of La3+,the formation of BF4-is mainly affected by LaF3 when pH is greater than 0,and in the case that the pH is lower than 2,it is mainly affected by HF2-.When Ce4+is present in solution,CeF22+ can exist stably in sulphuric acid solution.Bringing down the pH can reduce the stability of CeF22+ and increase the BF4-conversion rate.Based on these results,KBF4 was prepared in the alkaline solution of bastnaesite,and the conversion of BF4-is 84.31%.This provides a theoretical basis for the recovery of fluorine from bastnaesite in the form of KBF4. 相似文献
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《中国稀土学报(英文版)》2020,38(7):719-724
A series of VO_x/CeO_2 catalysts we re synthesized via vanadia supported on ceria with different BET surface areas.The catalysts were employed to investigate the active sites for the selective catalytic reduction of NO with NH_3(NH3-SCR).The kinetic results show that VO_x/CeO_2 catalysts exhibit nearly constant apparent activation energies(E_a),indicating the same SCR reaction mechanism.The V-O-Ce bridging modes and oligomeric VO_x were identified and quantified by Raman,FT-IR and H_2-TPR.The amounts of the V-O-Ce bridging modes calculated by H_2-TPR are correlated to the NH_3-SCR intrinsic reaction rates.The turnover frequencies(TOFs) show a constant value at the same temperature,which were calculated based on the number of V-O-Ce bridging modes of VO_x/CeO_2 catalysts.Therefore,it can be concluded that the V-O-Ce bridging modes are the active sites of VO_x/CeO_2 catalysts for the NH3-SCR reaction. 相似文献